Land reclamation method and equipment involving the introduction and mixing of a fluid and substances dispersed in air

ABSTRACT

A soil decontamination method uses a drilling rod having an outer pipe with a closed lower end and a radially extending outlet nozzle near the lower end. The outer pipe has an outer surface which is free of structures so that the outer pipe moves smoothly in a hole. An inner pipe is co-axially positioned in the outer pipe, the inner pipe having a lower closed end with a radially extending nozzle which is co-axial with, and spaced inwardly from the nozzle of the outer pipe. A drill bit is on an outer surface of a lower end of the outer pipe. A hole is drilled into a layer of soil using the bit. With the bit in the hole, a dry mixture of air and solid aggregate particles under relatively low pressure are supplied into a space between the outer and inner pipes and a high pressure fluid is supplied into the inner pipe under a relatively high pressure, the high pressure fluid leaving the nozzle of the inner pipe and taking with it some of the dry mixture which passes out of the outer pipe through the nozzle of the outer pipe to disaggregate and mix with and decontaminate soil of the layer around the hole.

FIELD AND BACKGROUND OF THE INVENTION

This invention relates to a land reclamation method which involves theintroduction and mixing of a fluid and substances dispersed in air, andthe related equipment.

In accordance with the method invented, the land is drilled to therequired depth with a probe fitted with at least one radial nozzle, apipe which supplies the said nozzle with a very high pressure fluid, anda second pipe through which a dry substance mixed with air is conveyed,forced out by the said high pressure fluid, and mixed with the soil.

The said pipes are preferably coaxial, and the high-pressure fluid isconveyed through the inner pipe.

Due to the high speed at which the mixture exits from the probe nozzle,a disintegration and mixing effect is produced which causes thesubstances required for the treatment to be evenly dispersed in thesubsoil layers; as a result, the soil is only treated at the requireddepth.

The invention is particularly suitable for the reclamation ofcontaminated soil.

The invention falls into the category of technologies applied to landreclamation, especially for treatment of subsoil layers designed todecontaminate or compact soil so as to create a layer with specificcharacteristics, such as a given degree of impermeability or the like.

Using the method in accordance with the invention, it is possible toinject into soil, or masses of refuse, substances which, by means ofphysical action (cementation) or chemical action, can stabilise the massso that it no longer represents a potential danger.

Cases of land pollution are increasingly frequent, especially close tocertain factories or sites used as tips for long periods.

The substances which percolate through the soil and are absorbed anddispersed in the subsoil layers often represent a serious source ofpollution, creating problems that are very difficult to solve.

The equipment currently used to reclaim this type of land consists oflarge helicoid screws fixed to the ends of rods which are inserted intothe soil and rotated to mix the soil with substances introduced duringthe advance of the unit.

This is obviously a very expensive system, whose efficacy is debatable.

For example, with this system it is impossible to treat only one layerof subsoil, e.g. to create an impermeable barrier or to decontaminate aspecific layer only.

The method does not allow the areas treated to be vertically isolated sothat the treatment only affects one layer of subsoil; the surface soilalso has to be mixed, involving a considerable waste of time and energyas well as high costs.

These known methods also present the drawback that they require veryhigh power to mix the deeper soil; large equipment therefore has to beused, but the results can hardly be considered perfect, especially asthese helicoids rotate at low speeds because they have to mix hugeamounts of soil.

In practice, using known reclamation methods it is impossible to treat aspecific layer of subsoil; the whole depth has to be treated because thescrew blades obviously have to penetrate all the soil layers, startingfrom ground level, to reach the zone in question.

SUMMARY OF THE INVENTION

To obviate this problem, this invention proposes a method (and theassociated equipment) whereby the soil is drilled with a probe (using asimilar system to the jet-grouting technique) and a fluid is injected atvery high pressure and speed (approx. 200-250 meters/sec.) through aradial nozzle; at the same time, substances mixed with a gas such as airare conveyed, sucked out by the fluid when it exits from the probe, andevenly distributed in the surrounding soil.

Techniques involving the injection of high-pressure fluids through aprobe with radial nozzles are already known; see, for example, Italianpatent application PC92A000002, which relates to a method ofconstructing consolidated cement columns in the soil into which ahigh-pressure cement grout (approx. 500 bars) is injected and grout orshotcrete is simultaneously injected at a lower pressure (approx. 20bars).

The injection is performed through a probe with coaxial radial nozzles.

However, this method is only designed for the mechanical consolidationof land, and no suggestion is made in that application about thepossibility of reclaiming land by injecting a high-pressure fluid orliquid mixture and simultaneously injecting gas mixed with liquid orsolid substances.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described in detail, by way of example butnot of limitation, by reference to the annexed figures in which:

FIG. 1 schematically illustrates the equipment in accordance with theinvention during the stage of decontaminating a layer of soil underneatha tip

FIG. 2 schematically illustrates a cross-section of a probe for use withthe method in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By reference to FIG. 1, the equipment required to implement the methodin accordance with the invention basically comprises a high-pressuremotor pump, shown as no. 1, an air compressor 2, a pressurized silo 3and downhole equipment 4.

The motor pump can pump a liquid at a pressure of approx. 500atmospheres along drill rod 5.

Compressor 2 sends a mixture of air and solid substances of suitableparticle size along rod 5.

Drill rod 5 (see FIG. 2) preferably consists of two coaxial pipes 6 and7.

The high-pressure fluid is pumped through inner pipe 6, while the airwith the aggregates is pumped through outer pipe 7.

Pipes 6 and 7 have one or more radially directed coaxial nozzles each atbit 8.

These nozzles are shown in the figure as nos. 9 and 10 respectively.

With this system, the high-pressure fluid will exit from nozzle 9 at avery high speed (approx. 200-250 meters/sec), drawing with it a certainmount of air mixed with the solid substance due to the Venturi effect.

The kinetic energy transmitted to the particles of solid matter enablesthem to disintegrate the soil and mix evenly with it.

Various experiments have established that if the drill rod has adiameter of 90 to 150 mm, and blast furnace ash is used at the rate of20 kg per cubic meter of air as the solid substance, good results areobtained with solids of a particle size not exceeding 4 mm, andpreferably between 2 and 3 mm.

Using this system (FIG. 1), the soil can be drilled down to layer 12 atthe required depth; the rod is then rotated, and the fluid and solidsubstances are simultaneously injected through pipes 6 and 7 to beginthe reclamation work.

The speed at which the rod rises and the distance between two adjacentdrilling points can be calculated on the basis of the type of soil andthe mount of substances to be mixed.

These figures, which obviously vary from case to case, are easilydetermined by an expert in jet-grouting technology.

The type of fluid and solid materials used depends on the job to beperformed.

Thus in order to consolidate soil and regulate its acidity, a mixture ofwater and cement could be pumped through pipe 6, and air mixed withblast furnace ash directed through pipe 7.

In particular, tests have been conducted on soil used for decades as atip, which presented a very low density and a pH of 13.4.

By injecting 12 cu.m/min. of air with a content of 20 kg/cu.m. of blastfurnace ash, and simultaneously injecting a mixture of water and cementat the rate of 250 liters/min., the pH of the soil was adjusted to 8.1,and a good density obtained at the same time.

For decontamination operations, high-pressure water and air mixed withbacteria could be pumped through the inner and outer pipes respectively.

In particular, a bacterial culture substrate could be injected at highpressure, and the bacteria dispersed in the soil through thelow-pressure pipe.

Here again, tests have been conducted with lyophilised "BIO ACTIV BP"bacteria (hydrocarbon degradation bacteria) produced by T.B.A.Techniques et Biotechnologies Appliquees of Paris.

In particular, the bacteria count of soil into which high-pressure waterand a current of air in which lyophilised bacteria are dispersed at therate of 20 kg/cu.m has been tested, to establish the compatibility ofthe method with the use of bacteria.

In other cases, high-pressure hydrogen peroxide and air mixed with metalsulphides in the outer pipe could be injected to oxygenate the soil.

Basically, the method in accordance with the invention involves the useof techniques similar to the jet-grouting technique to treat deep-lyinglayers of soil of limited thickness, by injecting a high-pressure fluidand a quantity of solid substances mixed with air at a lower pressureinto the soil through a pair of coaxial nozzles, so that thehigh-pressure fluid draws the air-aggregate mixture with it due to theVenturi effect, dispersing it in the soil layer.

This system produces excellent reclamation results with relativelymodest equipment and no need to treat the surface soil, as the injectionof the substances can be restricted to the thickness of the soil layerto be treated.

An expert in the field could devise numerous modifications andvariations, all of which should be considered to fall within the scopeof this invention.

I claim:
 1. A soil decontamination method comprising:providing adrilling rod having an outer pipe with a closed lower end and a radiallyextending outlet nozzle near the lower end, the outer pipe having anouter surface which is free of outer structures; providing an inner pipeco-axially positioned in the outer pipe, the inner pipe having a lowerclosed end with a radially extending nozzle which is co-axial with andspaced inwardly from the nozzle of the outer pipe; providing a drill biton an outer surface of the lower end of the outer pipe; drilling a holeinto a layer of soil using the outer pipe and drill bit; with the outerpipe and drill bit in the hole, supplying a dry mixture of air and solidaggregate particles under relatively low pressure into a space betweenthe outer and inner pipes; and supplying a high pressure fluid into theinner pipe under a relatively high pressure, the high pressure fluidleaving the nozzle of the inner pipe and taking with it some of the drymixture which passes out of the outer pipe through the nozzle of theouter pipe to disaggregate and mix with decontaminate soil of the layerwhich is around the hole.
 2. A method according to claim 1 wherein theaggregate comprises particles having a particle size from about 2-3 mm.3. A method according to claim 2 wherein the high pressure fluid issupplied at a rate of about 200-250 meters per second.
 4. A methodaccording to claim 3 wherein the outer pipe has a diameter of about90-150 mm.
 5. A method according to claim 4 wherein the aggregatecontains blast furnace ash.
 6. A method according to claim 5 whereinblast furnace ash is supplied at a rate of about 20 kg per cubic meterof air.
 7. A method according to claim 6 wherein the high pressure fluidof the inner pipe is a mixture of water and cement.
 8. A methodaccording to claim 1 wherein blast furnace ash is supplied at a rate ofabout 20 kg per cubic meter of air.
 9. A method according to claim 8wherein the high pressure fluid of the inner pipe is a mixture of waterand cement.
 10. A method according to claim 9 wherein the aggregatecomprises particles having a particle size from about 2-3 mm.
 11. Amethod according to claim 10 wherein the high pressure fluid is suppliedat a rate of about 200-250 meters per second.
 12. A method according toclaim 11 wherein the outer pipe has a diameter of about 90-150 mm.